1. Field of the Invention
The present invention concerns a method for operation of a flash smelting furnace, in particular, for smelting non-iron metals.
2. Description of the Prior Art
A flash smelting furnace has been known as one of refining furnaces using sulfide concentrates as a raw material. FIG. 3 shows an example of a structure of the flash smelting furnace of this kind, which is referred to as an Outokumpu type flash smelting furnace. In the figure, the flash smelting furnace 1 basically comprises a reaction shaft 3 having a concentrate burner 2 disposed at the top, a settler 6 connected at one end thereof to the lower portion of the reaction shaft 3 and having a slag discharge port 4 and a matte discharge port 5 disposed on the side thereof and an uptake 7 connected to the other end of the settler 6. In the operation of such an Outokumpu type flash smelting furnace, a smelting raw material 8 such as a sulfide concentrate, a flux and an auxiliary fuel is at first blown together with a portion of a reaction air by way of the concentrate burner 2 into the reaction shaft 3. In the reaction shaft 3, sulfur and iron as the combustible components of the smelting raw material 8 heated by the combustion of the auxiliary fuel are brought into reaction with the reaction air 9, which is also heated, and then accumulated in a molten state in the settler 6. Further, the melt accumulated in the settler 6 as a hearth is separated by the difference of the specific gravity of the ingredients thereof into a matte 10 consisiting of a mixture of Cu.sub.2 S and FeS and a slag 11 mainly composed of 2FeO.SiO.sub.2. The slag 11 is discharged from the slag discharge port 4 and introduced into an electric slag cleaning furnace 12, while the matte 10 is properly discharged from the matte discharge port 5 in accordance with a demand from a converter in the subsequent step. The slag 11 entering the electric slag cleaning furnace 12 is kept to be heated by a heat generated from electric current supply from an electrode 13 and mixed with ore lumps, flux lumps, etc. charged as required to the electric slag cleaning furnace 12, in which the copper component is deposited further to the bottom of the furnace and only the slag containing a slightly remaining copper component is discharged from the outlet 14 to the outside of the furnace. A waste gas 15 at high temperature emanated in the reaction shaft 3 is sent by way of the settler 6 and the uptake 7 and then cooled by a waste heat boiler 16.
In the Outokumpu type flash smelting furnace, since the control for the oxidation degree of the smelting raw material and the control for the smelting temperature can be conducted independently of each other, it is suitable to refining plants using commercial ores in which the compositions of the raw materials vary inevitably.
However, in such a conventional flash smelting furnace, there has been a problem that no sufficient heat calorie required for melting the smelting raw material 8 can be obtained. That is, the residence time for the particles of the smelting raw material 8 blown by way of the concentrate burner 2 is usually about one second, during which the particles have to be melted by heating to the ignition temperature thereof and being brought into reaction with oxygen in the reaction air 9. Then, although it is necessary to preheat the reaction air 9 to the ignition temperature quickly, the upper limit for the temperature of the reaction air 9 is restricted to 400.degree.-500.degree. C. in view of the relation with the heat resistant temperature of materials for the facilities of the smelting furnace and no sufficient pre-heating can be applied, with a result that the rate of dust generation is increased, as well as the oxygen utilization ratio, that is, oxygen efficiency is inevitably lowered.
In view of the above, a method of using an oxygen enriched air as a reaction air has been put to practical use in order to overcome such a problem. For instance, according to a device disclosed in Japanese Patent Publication Sho 59-41495, improvement is intended for the oxygen efficiency, while taking notice on the high reactivity between an industrial oxygen and a sulfide concentrate by blowing an oxygen-enriching oxygen entirely or partially into a concentrate shoot, while supplying air or an oxygen enriched air from a venturi portion of a concentrate burner, thereby uniformly mixing and dispersing the smelting raw material such as the sulfide concentrate and oxygen.
On the other hand, if the mixing between the smelting raw material blown from the concentrate burner 2 into the reaction shaft 3 of the furnace 1 and an oxygen-enriching oxygen or oxygen-enriched reaction air is insufficient, the utilization efficiency of oxygen reacting with the smelting raw material, that is, the oxygen efficiency is lowered. If the oxygen efficiency is low, it is necessary to supply an oxygen-enriching oxygen or oxygen-enriched reaction air in an amount than required, which leads to the increase of an auxiliary fuel for elevating the temperature of the reaction air supplied in excess and to the increase of the rate of dust generation along with the increase of the amount of waste gases.
For overcoming such a problem, there can be mentioned prior art in, for example, Japanese Utility Model Laid-Open Hei 1-78161 and Hei 1-78162 and the Japanese Patent Laid-Open Hei 2-236234.
Japanese Utility Model Laid Open Hei 1-78161 and Hei 1-78162 describe a concentrate burner comprising an air supply tube, a venturi portion concentrically joined to the lower surface at one end of the air supply tube and a concentrate shoot vertically penetrating the end of the air supply tube from above and extended concentrically to the venturi portion, in which a reaction air supplied from the air supply tube passing between the concentrate shoot and the venturi portion is blown into the top of the reaction shaft (hereinafter referred to as a conventional concentrate burner), wherein one or two blow control plates are disposed in the air supply tube in adjacent with the venturi portion so that the reaction air is blown uniformly from the venturi portion.
Further, in Japanese Patent Laid Open No. Hei 2-2326234, at least one set of air supply nozzles are disposed near the middle portion of a reaction shaft each at a 180.degree. symmetrical position with respect to a vertical line passing through the center of the reaction shaft, such that the axial blowing direction of each of the nozzles aligns with the vertical line, and each of the nozzles is made rotatable within a vertical plane including the axial blowing direction of the nozzle. A portion of a reaction air is blown from the nozzles to form a turbulent flow over the entire region in the reaction shaft, so that the smelting raw material flown from the concentrate burner into the reaction shaft is uniformly dispersed in the reaction air and the residence time thereof in the reaction shaft is prolonged, by which the smelting raw material such as the concentrate ore and the reaction air can be effectively brought into reaction and the oxygen efficiency of the reaction air can be improved further, with a result that the rate of dust generation can be reduced and the formation of unmelts can be prevented.
However, in the device as disclosed in Japanese Patent Publication Sho 59-41495, since oxygen for oxygen enrichment is jetted into a concentrate shoot, sulfide concentrates are brought into reaction with oxygen in the concentrate shoot and fused to the inside of the shoot to clog the concentrate shoot thereby making continuous operation impossible. Further, in this device, since concentrate particles are sufficiently suspended in an oxygen gas stream, satisfactory reaction is taken place in the furnace. However, since the gas stream does not spread, concentrate particles are liable to be discharged together with exhaust gases containing SO.sub.2 generated by combustion to the outside of the furnace, which brings about a disadvantage that not only the rate of dust generation can not be reduced but also the generation rate is rather increased depending on the operating conditions.
The device as disclosed in Japanese Utility Model Laid-Open Hei 1-78161 and Hei 1-78162 comprise a flow control plate disposed for making the uniform blowing of the reaction air from the venturi portion in the conventional concentrate burner and it can sufficiently enjoy the performance of the conventional concentrate burner. However, the performance of the conventional concentrate burner is only that the rate of dust generation is more than 9% and the oxygen efficiency is less than 80%, and no better performance can be expected.
According to the examples in Japanese Patent Laid-Open Hei 2-230234, it has been reported that the rate of dust generation is 5.8% and the oxygen efficiency is 100% as the best result obtained in the operation. Then, it is apparent that the flash smelting furnace and the operating method according to this invention are excellent over the flash smelting furnace and the operating method using the conventional concentrate burner. However, according to the study made subsequently, it has been apparent that if the ratio of the silicate ore added other than the sulfide concentrate as the smelting raw material is increased in the operation of the example, although the rate of dust generation did not change so much but the oxygen efficiency was reduced. This is assumed to be attributable to the following reasons.
In accordance with this operating method, since a portion of the reaction gas is blown from an air supply nozzle and hit against a jet stream formed by the concentrate burner, to form a turbulent flow spreading over the entire region in the reaction shaft, the smelting raw material blown together with the auxiliary fuel and the reaction air from the concentrate burner into the reaction shaft is uniformly dispersed in the reaction air. In this case, silicate ore, powdery iron concentrate, copper slag, dust or the like, other than the sulfide concentrate added as the smelting raw material are non-combustible substances, which hinder the combustion of the concentrate ore in the reaction shaft. Among all, since the silicate ore has the main ingredient SiO.sub.2 the melting point of which is as high as 1720.degree. C., it is apparent that the combustibility of the concentrate ore is greatly hindered. In this operating method, since the concentrate ore under combustion and silicious sand are uniformly dispersed in the reaction shaft as the ratio of the silicate ore added is increased, the silicate ore acts as if it were a powdery fire extinguishing agent. This results in the lowering of the temperature of the concentrate particles under combustion, which suppresses the oxidizing reaction of the concentrate ore itself to reduce the oxygen efficiency.